The present invention relates to an improved medical appliance for ultrasonic therapeutic treatment and/or other operation upon living body tissue.
The application of ultrasound in diagnostic scanning techniques and therapeutic treatment of specific medical conditions has been widely reported in the technical literature over the last 20 to 30 years. However, prior to application GB 2274996A, which does disclose treatment apparatus operating in the kHz band, no relevant reference was found, for the use of frequencies in the range 30 to 100 kHz.
It is known that ultrasound therapeutic radiation in the MHz band has beneficial effects when treating soft-tissue injuries, and that such emissions are absorbed (attenuated) to differing degrees in different types of living tissue.
This characteristic of absorption or attenuation limits to some extent the scope for treating certain types of injury since in order to transmit adequate intensities of radiation to a deep injury, potentially harmful levels would have to be introduced into the outer tissue layers. To overcome this problem of natural attenuation at greater depth of injury, it has previously been proposed to use long-wave radiation in the 45 to 50 kHz band, with correspondingly improved transmission characteristics. This is described in U.S. Pat. No. 5,549,544, the disclosure of which is hereby incorporated by reference. It suffices here to note that said disclosure pertains to the use of a single excitation frequency in the range 20 to 120 kHz and to the employment of a body-contacting application head having a specific impedance (W) that closely matches that of human soft tissue.
The use of frequencies in the MHz band stems from the concept that therapeutic treatment using ultrasonic energy should be directed accurately to a well-defined region of tissue and that this is best achieved with a finely focused beam. However, it is often necessary to apply a broader range of treatment, and in this case, a mixture of comparatively higher and lower frequency vibrations is to be desired. For example, the characteristic wavelength corresponding to a 3 MHz transmission through soft tissue is about 0.5 mm; but at 40 kHz, the wavelength would be approximately 37.5 mm.
The combination of wavelengths, however achieved, will give a more even distribution of energy within the tissue being treated. Also, in cases where only local treatment, or treatment of an area close to the surface, is required, there is still a need for a treatment device which can selectively treat chosen areas.
However, since it is known that the attenuation of ultrasonic waves increases with increasing frequency, the general effect of high-frequency transmission is to produce relatively high energy-absorption rates close to the entry surface, and for the effect to fall off with increasing depth. It may therefore be concluded that, for a given power input, it is preferred to use a low-frequency input when treating deep-tissue injuries. This consideration becomes very important since in order to transmit enough energy to the required region, the risk of excessive absorption in surface layers may become unreasonably high when applying therapeutic ultrasound in the MHz band. For this reason, energy levels are limited by the requirement that intensity should not exceed 3 watts/cm2.
Furthermore, conventional high frequency systems produce columnar (collimated) energy beams which can lead to a danger of standing waves, internal reflection and consequent hot spots in irradiated tissue. In contrast to this, longer wavelength transmissions exhibit a spherical wavefront, with diverse propagation characteristics and little or no risk of standing waves.
It is an object of the present invention to provide improved ultrasonic means for combining benefits associated with long-wavelength treatment with those associated with shorter wavelength treatment.
According to one aspect of the present invention, apparatus is provided to treat muscular injuries within or below a body surface or to diagnose bone fractures, wherein the device comprises piezoelectric means to generate ultrasonic energy, said piezoelectric means comprising at least two generator means each adapted to deliver energy at a different frequency in the range 10 kHz to 4 MHz, a first application head adapted to be applied closely to the body surface and to deliver thereto energy from one of said generator means, and a second application head adapted to be applied closely to the body surface and to deliver energy thereto from another of said generator means.
Preferably, a first or low-frequency generator means provides energy at a frequency in the range of between, 10 to 110 kHz, advantageously 20 to 100 kHz and preferably in the region of 45 kHz.
Advantageously, a second or high-frequency generator means generates energy at a frequency in the region of 0.5 to 4 MHz, advantageously 0.5 to 3 MHz, and preferably in the region of 1 MHz.
In a preferred embodiment, the body-application heads for the respective generator means are adapted for location in spaced mutual adjacency at adjacent portions of a treatment surface of the apparatus, wherein the spacing provides an important degree of acoustic isolation between the respective heads.
At least the low-frequency application head may be machined or molded from a range of dense polymers including acetal, polypropylene and polycarbonate. These and similar materials all permit the transmission of low-amplitude ultrasound in the frequency range 30 to 100 kHz, with relatively low energy absorption. The head is machined from plastics material which is chosen because its specific impedance (W) closely matches that of human soft tissue.
As an example, acetal may be used, in which case applicable figures are:
Wacetal=1.86xc3x97106 Kg Mxe2x88x922secxe2x88x921;
Wsoft tissue=1.65xc3x97106 kg Mxe2x88x922secxe2x88x921.
According to another aspect of the present invention, there is provided a method of treating muscular injuries or of diagnosing bone fractures, wherein the method comprises applying to an external surface of the tissue, two component sources of acoustic energy, each component having a different frequency in the range between 10 kHz and 4 MHz, and each component being applied independently to adjacent but separate portions of the external surface of a patient""s body.
According to a further aspect of the invention, there is provided a surgically non-invasive method of treating deep-seated muscular injuries or of diagnosing bone fractures, wherein the method comprises the steps of applying to an external surface portion of the tissue an application head which comprises a first member capable of emitting acoustic energy, generally symmetrically about a directional axis and at a comparatively low frequency and independently applying acoustic energy at a relatively high frequency to an adjacent portion of the surface and with general symmetry about said axis.